Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$54.68	6.618%	$58.2987	$58.30	$58.30	$58.30
Purchase #2	$173.91	12.839%	$196.2383	$196.24	$196.25	$196.20
Purchase #3	$78.38	13.233%	$88.752	$88.75	$88.75	$88.80
Purchase #4	$153.82	12.167%	$172.5353	$172.54	$172.55	$172.50
Purchase #5	$92.50	7.595%	$99.5254	$99.53	$99.55	$99.50
Purchase #6	$101.80	12.810%	$114.8406	$114.84	$114.85	$114.80
Purchase #7	$145.59	10.640%	$161.0808	$161.08	$161.10	$161.10
7 purchase totals =	$800.68		$891.2711	$891.28	$891.35	$891.20